Venturi-type mixing devices, sometimes referred to as eductors, use aspiration to mix two liquids. An eductor directs a pressurized stream of a first liquid (usually water) through a venturi. A second inlet passage extends from a storage vessel (that holds a second liquid, e.g. a surfactant) to the downstream end of the venturi. A difference in pressure between the storage vessel and the eductor venturi outlet causes the second liquid to be drawn into the water stream.
Building custodial staffs use dispensing equipment to dilute surfactant concentrates and then dispense them. The concentrates are stored in vessels in the equipment, or are connected to the equipment by hoses. The equipment often includes eductor systems of the above type to dilute the concentrate to form cleaning solutions. The resulting solutions are then directed into a bottle, pail, bucket, or the like that will be used by the custodial staff to carry the cleaner.
One manufacturer of such dispensing equipment (sold under the trademark SOLUTIONS CENTER.RTM. and other trademarks) and liquid concentrates used therewith is S. C. Johnson & Son, Inc. of Racine, Wis. An eductor of the type used in SOLUTIONS CENTER.RTM. equipment is described in PCT Publication No. W091/16138 and U.S. Pat. No. 5,544,810 (Horvath et al.). Hand held dispensing/diluting equipment is also known. See e.g. U.S. Ser. No. 08/668,051. All applications and all publications referred to herein are incorporated herein by reference as if fully set forth. Concentrates used with such equipment have included a neutral cleaner, a "spray-and-wipe" cleaner/degreaser, a glass cleaner, and various other concentrates.
Such dispensing devices are not without some disadvantages when high foaming surfactants are used. In this regard, if a dilute solution of a cleaner is formed or delivered in a way that causes excessive foam, a container receiving the solution can overflow with foam even though only a small quantity of the solution has been added to it. This can cause undesirable delays during filling (e.g., while the user waits to let the foam subside). In some cases the delay can cause the user to "give up" in frustration and accept a partially filled container.
Complicating the design of improved dispensing systems is the need for the use of backflow protection. Plumbing codes require a means to protect the water supply from contamination due to backflow. This can be accomplished with various devices and combinations of them including mechanical vacuum breakers, check valves and air gap devices. Air gap devices are very attractive because they have no moving parts to malfunction, but they can add air to the water stream during operation. The addition of air to a water stream can exacerbate foaming.
It can therefore be seen that a need exists for an eductor which overcomes these shortcomings.